Knob with different gear ratios

ABSTRACT

A knob adjustment device particularly for adjusting the temperature in valve units for water-heating apparatus is described and comprises geared movement-transmission means interposed between the knob ( 2 ) and an operating member ( 4 ) of the valve unit in order to transmit a rotary movement to the member about its own axis as a result of a rotation of the knob. The geared transmission means comprise reduction means ( 5,6,7,8 ) with a variable transmission ratio such that, for a first angular portion (C) and a second angular portion (D) of the rotation of the knob, the member is rotated with respective different transmission ratios (T 1 ,T 2 ).

TECHNICAL FIELD

[0001] The present invention relates to a knob adjustment device,particularly for temperature adjustment in water-heating apparatus,according to the preamble to the main claim.

[0002] The invention relates, in particular but not exclusively, to thefield of water-heating apparatus such as, for example, a domesticwater-heater having a thermostatic valve unit with a knob adjustmentdevice for adjusting the temperature to which the water is to be heated.

BACKGROUND ART

[0003] In these units it is desirable to operate with a single valveseat associated with a respective closure element which has both thefunction of shutting off the gas flow (ON/OFF) and the function ofadjusting the flow to achieve the water temperature desired by the user.In this connection, the valve unit has a knob adjustment deviceoperatively connected to the closure element by means of a controlmember with which the user can enable the function of lighting a pilotburner or of shutting off the gas-flow (OFF) and, in addition, canselect a preselected water-temperature value.

[0004] When the above-mentioned functions are incorporated in a singledevice, it is also desirable to be able to perform these functions atmost by a single rotation of the knob, in order to achieve quicker andeasier use by the user. However, in addition to the angulartemperature-selection band (normally an adjustment within the rangebetween approximately 30° C. and 70° C. is required), it is thereforenecessary also to provide an angular band on the knob for regulating theshut-off (OFF) and pilot-burner lighting points. This therefore reducesthe angular band available for temperature selection, which translatesinto a lower degree of resolution within the above-mentioned range ofbetween approximately 30° C. and 70° C. such that the user cannot adjustthe temperature with a sensitivity, for example, with variations of theorder of one degree centigrade in the preselected temperature values.

[0005] The problem upon which the present invention is based is that ofproviding a knob adjustment device which is designed structurally andfunctionally so as to overcome the disadvantages complained of withreference to the prior art mentioned.

DISCLOSURE OF THE INVENTION

[0006] This problem is solved by the invention by means of a knobadjustment device of the type indicated and formed in accordance withthe appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0007] The characteristics and the advantages of the invention willbecome clearer from the following detailed description of a preferredembodiment thereof, described by way of non-limiting example, withreference to the appended drawings, in which:

[0008]FIG. 1 is a schematic perspective view of a valve unit equippedwith a knob adjustment device formed in accordance with the presentinvention,

[0009]FIGS. 2 and 3 are a perspective view and a plan view from below,of the knob adjustment device of FIG. 1, respectively, and

[0010]FIG. 4 is a graph showing the rules governing temperaturevariation as a function of the angular rotation of the knob device ofthe previous drawings.

BEST MODE OF CARRYING OUT THE INVENTION

[0011] With reference to FIG. 1, a valve unit, generally indicated 1, isequipped with a knob adjustment device 2 formed in accordance with theinvention. In the embodiment described, the valve unit 1 is of thethermostatic type and is intended mainly for the adjustment and controlof the water temperature in heating apparatus, for example, in domesticwater-heaters. However, the device according to the invention isintended also to be usable in other fields, although the field indicatedrepresents a preferred selection.

[0012] The valve unit 1 has an element 3 sensitive to the variation ofthe water temperature and operatively connected to a closure element,not shown, in order to cause the latter to close/open a respective valveseat, also not shown, inside the unit.

[0013] The knob 2 is mounted so as to be rotatable on the unit 1 about arotation axis X and is kinematically connected, by means of a gearedtransmission system, to an operating member 4, also supported so as tobe rotatable on the unit 1, about a rotation axis Y. The axes X and Yare perpendicular to one another.

[0014] The operating member 4 is in turn associated with an actuatormeans of conventional type which acts on the closure element of thevalve unit in order to perform the functions of shutting off the mainflow of gas through the unit 1 as well as of adjusting the temperaturevalue by the thermostatic closure of the respective valve seat when thepreselected temperature set by the user is exceeded.

[0015] More particularly, the functions of temperature adjustment, ofenabling a pilot burner associated with the heating apparatus to be lit,as well as of completely shutting off the gas flow (OFF point) suppliedto the unit, are combined in the knob device 2.

[0016] In the knob device, the geared transmission system is intended totransmit a rotary movement to the operating member 4, about its own axisY, as a result of a rotation of the knob 2 about the axis X.

[0017] The geared transmission system is of the crown-wheel and piniontype and comprises a pair of coaxial crown wheel sectors 5, 6 fixed forrotation with the knob 2, as well as a pinion 7, coaxial and fixed forrotation with the operating member 4, and capable of meshing with thecrown wheel sectors 5, 6.

[0018] The crown wheel sectors 5, 6 are of the type with face teeth andextend concentrically substantially as extensions of one another buthaving different respective diameters.

[0019] The sectors 5, 6 are also spaced apart circumferentially in amanner such that the pinion 7 meshes alternatively with one or other ofthe crown wheel sectors.

[0020] Moreover, an intermediate tooth 8 (or several teeth), interposedbetween the crown wheel sectors and extending concentrically with thesectors 5, 6 along an arc having a diameter between the diameters of thesectors, can also mesh with the pinion 7.

[0021] The tooth 8, as well as the crown wheel sectors 5, 6, are spacedapart circumferentially. The angular distances between the tooth 8 andthe respective ends of the sectors 5, 6 closest to the tooth areindicated A and B in FIG. 3 and the angular amplitudes of the crownwheel sectors 6 and 5 are indicated C and D.

[0022] For a first angular portion and a second angular portion whichare consecutive and correspond, respectively, to the sectors 5 and 6,the pinion 7 is thus rotated by the knob 2 with a first transmissionratio and with a second transmission ratio T1, T2, respectively (definedas the ratio between the diameter of the pinion 7 and the diameter ofthe respective crown wheel sector 5, 6).

[0023] According to a preferred characteristic of the device accordingto the invention, the transmission ratio T1 is selected so as to beapproximately three times the transmission ratio T2. Moreover, thetransmission ratio, indicated T3, between the tooth 8 and the pinion 7is selected so as to have an intermediate value between the transmissionratios T1 and T2.

[0024] The graph of FIG. 4 shows the curve of the temperature (on theordinate) as a function of the angular rotation band provided on theknob (on the abscissa).

[0025] The angular amplitude D is representative of the band for theselection of the temperature within the preselected range ofapproximately 30° C. to 70° C. and the slope of the curve (FIG. 4) inthis portion is correlated directly and proportionally with thetransmission ratio T2 with which the member 4 is rotated by the knob 2along the crown wheel sector 5.

[0026] The angular amplitude C, on the other hand, is representative ofthe angular band required to set the temperature for the opening of themain gas duct at a temperature lower, by a suitable safety margin, thanthe minimum temperature of use of the apparatus. In this portion, theslope of the curve is correlated directly and proportionally with thetransmission ratio Ti by which the operating member 4 is rotated by theknob 2 along the crown wheel sector 6.

[0027] It will be noted that the change in transmission ratio enables aconsiderably smaller angular band to be achieved for lighting andshutting off (angular distance C) than can be achieved with equaltransmission ratios (equal to T2).

[0028] All of the above-mentioned functions implemented in the knobdevice 2 can thus be set by the user within a single rotation of theknob. A preferred value for the angular rotation of the knobcorresponding to the sum of the angular amplitudes A, B, C and D isbetween 225° and 340° and is preferably selected so as to be 315°.

[0029] Moreover, the temperature selection band (the angular amplitudeD) can advantageously be kept within an angular rotation of the knob ofthe order of about 150° so as to permit an adequate resolution andgreater sensitivity in the setting of the temperature values by theuser. The angular amplitude C is consequently reduced to a value ofabout 120° by virtue of the provision of the transmission ratio T1.

[0030] It will also be noted that the changeover of the pinion 7 betweenits meshing with the crown wheel sector 6 and with the sector 5 takesplace via an intermediate meshing with the tooth 8 so as to permitsmoother and more continuous rotation of the knob. In fact, the pinion 7is arranged not to mesh with both of the crown wheel sectors 5, 6 at thesame time but changes over between the sector 6 and the tooth 8 andbetween the tooth 8 and the sector 5 by respective successive meshings.The discontinuity of rotation due to the different peripheral velocitiesof the mutually meshed teeth during the instantaneous change oftransmission ratio is thus considerably reduced. The provision of theintermediate transmission ratio T3 thus reduces the effects due to thediscontinuity of rotation and advantageously enables a ratio Tiapproximately three times the ratio T2 to be achieved.

[0031] The invention thus solves the problem set, achieving theadvantages mentioned above.

[0032] In particular, the knob adjustment device of the inventionenables all of the adjustment and temperature-selection functionsprovided for to be incorporated in the valve unit with a operativeangular band less than or equal to one complete rotation of the knob,for easier and quicker use by the user, at the same time ensuring anadequate degree of resolution and sensitivity for the user in theselection of the preselected temperature value.

1. A knob adjustment device, particularly for adjusting the temperaturein valve units for water-heating apparatus, comprising gearedmovement-transmission means interposed between the knob (2) and anoperating member (4) of the valve unit in order to transmit a rotarymovement to the member (4) about its own axis as a result of a rotationof the knob (2), said geared transmission means comprising reductionmeans (5-8) with a variable transmission ratio such that, for a first(C) and a second (D) angular portion of the rotation of the knob (2),said member is rotated with respective and different transmission ratios(T₁, T₂), said reduction means comprising a pair of crown wheel sectors(5, 6) having face teeth, coaxial with and fixed for rotation with theknob (2), said crown wheel sectors being concentrically extended,substantially as extensions of one another with respective differentdiameters, and being able to mesh with a pinion (7) fixed for rotationwith the operating member (4), characterized in comprising, between saidcrown wheel sectors, at least one tooth (8) radially disposed in aposition between the crown wheel sectors (5,6) and able to mesh with thepinion (7).
 2. A device according to claim 1, in which said crown wheelsectors (5, 6) and said at least one intermediate tooth (8) are spacedapart circumferentially in a manner such that said pinion (7) meshesalternatively with one or other of the respective crown wheel sectors(5,6) or with the at least one intermediate tooth (8).
 3. A deviceaccording to claim 1 or 2, in which said at least on tooth (8) extendsconcentrically with the sectors (5,6) along an arc with a diameterhaving an intermediate value between the diameters of the crown wheelsectors.
 4. A device according to one or more of the preceding claims,in which said crown wheel sectors (5, 6) and the at least oneintermediate tooth (8) have a circumferential extent such that theoperating member (4) is rotated for a first angular portion and a secondangular portion consecutive (C,D), with a respective first and secondtransmission ratio (T₁,T₂), the transmission ratio (T₁) between thefirst crown wheel sector (5) and the pinion (7) being approximatelythree times of the transmission ratio (T2) between the second sectors(6) and the pinion (7).
 5. A device according to claim 4, in which thetransmission ratio between the intermediate tooth (8) and the pinion (7)is an intermediate ratio (T₃) between the transmission ratios (T₁,T₂) ofthe crown wheel sectors (5,6).